1. Field of the Invention
The present invention relates to mobile wireless devices for mobile location systems, and more particularly to Global Positioning Satellite (GPS) receivers with improved indoor penetration for personal location systems.
2. Description of the Related Art
With the advent of GPS, there has been a growing demand for mobile devices that may be used to provide a person's or an object's location. Devices built using conventional GPS receivers have been developed by a number of companies. However, these devices have significant limitations, one of which is indoor penetration.
To address the above limitation of conventional GPS receivers, a combination of mobile GPS receivers and cellular infrastructure communicating via wireless links has evolved. This combination of technologies, known as Assisted GPS (AGPS), combines a GPS receiver with a cellular handset. The cellular handset provides a two-way link for communicating positioning data (“aiding data”).
In particular, performance of a conventional GPS mobile device in indoor environments may be limited by ability of the GPS mobile device to decode a navigation data stream broadcast by each of a plurality of satellites. Among other components, each navigation data stream contains a satellite trajectory model having parameters describing a respective satellite's orbit and clock variation as a function of time. The satellite trajectory model in the navigation data stream is sometimes referred to as “broadcast ephemeris.” GPS mobile devices traditionally receive and decode the navigation data stream to extract the broadcast ephemeris, which is needed to compute position. However, a signal-to-noise ratio in indoor environments is often insufficient for navigation data bit decoding of the broadcast ephemeris. Thus, another means of ascertaining satellite orbit and clocks variations was needed.
In AGPS systems, the satellite orbit and clock variation, or information derived from these components, is provided to the GPS mobile device via a two-way cellular link. A two-way cellular link is used to request and receive information on such satellites, and the AGPS service is conventionally available only to authorized subscribers to a cellular network.
While AGPS offers improvements in indoor penetration, addition of a cellular handset and a subscription to a wireless provider adds to the cost and power consumption of a GPS receiver. Cellular handsets contain complex and costly components. For example, the cost of adding a cell phone alone to a GPS receiver may be prohibitive for GPS applications where a phone would otherwise be an unnecessary addition, let alone the addition of a subscription fee of a cellular provider. Moreover, cellular transmission consumes power.
Therefore, it would be desirable to provide a GPS mobile device that is comparable in cost to conventional GPS handheld devices but with the indoor penetration benefits associated with AGPS handsets.